1. Field of the Invention
The invention is generally related to the area of optical communications. In particular, the invention is related to method and apparatus for a single optical module for multiplexing/demultiplexing optical signals by using wedges to bond various components to one or more common substrates.
2. The Background of Related Art
The future communication networks demand ever increasing bandwidths and flexibility to different communication protocols. WDM (Wavelength Division Multiplexing) is one of the key technologies for such optical fiber communication networks. WDM employs multiple wavelengths in a single fiber to transmit in parallel different communication protocols and bit rates. Transmitting several channels in a single optical fiber at different wavelengths can multi-fold expand the transmission capacity of the existing optical transmission systems, and facilitating many functions in optical networking. An international standard wavelength grid has been suggested by ITU (International Telecommunication Union) for the center wavelengths of DWDM systems. Different technologies have been developed to divide or combine channels or subgroups of channels in the ITU grid.
From a terminology""s viewpoint, a device that multiplexes different wavelength channels or groups of channels into one fiber is a multiplexer, and a device that divides the multiplexed channels or groups of channels into individual or subgroups of channels is a demultiplexer. Specifically, when a multiplexer combines several channels of optical signals into a single signal, or in reverse a demultiplexer separates a single multichannel signal into several individual channel signals, such multiplexer/demultiplexer is referred to a multiplexing/demultiplexing module, or simply multiplexer or demultiplexer.
Known devices for multiplexing/demultiplexing have employed, for example, diffraction gratings, arrayed waveguide gratings and various types of fixed or tunable filters. Gratings typically require complicated alignment systems and have been found to provide poor efficiency and poor stability under changing ambient conditions. Fixed wavelength filters, such as interference coatings, can be made substantially more stable, but transmit only a single wavelength or wavelength band.
U.S. Pat. No. 5,583,683 to Scobey discloses an optical multiplexing device that spatially disperses collimated light from a fiber optic waveguide into individual wavelength bands, or multiplexes such individual wavelength bands to a common fiber optic waveguide or other destination. An optical block has an optical port for passing multiple wavelength collimated light to be demultiplexed. Multiple ports are arrayed in spaced relation to each other along a multiport surface of the optical block to receive respective the individual wavelength bands. With respective collimators that must be precisely coupled to the multiple ports, the optical multiplexing device can be bulky, expensive and susceptible to varying ambient conditions (e.g. temperature and vibrations).
There has always been a need for an optical multiplexing device that is small in size, low in cost, and remains stable in varying working conditions.
The present Invention pertains to improved designs of optical multiplexing/demultiplexing module used to demultiplex a composite optical signal into respective individual channels or wavelengths or to multiplex individual channels or wavelengths into a composite optical signal. According to one aspect of the present invention, the optical multiplexing/demultiplexing module comprises an array of collimators, an array of optical filters and an array of mirrors. The collimators are bonded to a common substrate after being aligned with a respective optical filter. Different from the prior art devices, the aligned positions of the collimators are secured or held up by preformed wedges. A bonding agent is then applied only to respective contacts between the collimators and the wedges. The wedges are further bonded to a common substrate to secure the collimators. In one embodiment, the optical filters as well as the mirrors that have been aligned with the collimators may be also bonded to the substrate. As a result, integrated multiplexing/demultiplexing modules can be configured small in size and easy to be assembled or manufactured. Because all components are bonded or fixed to one or more common substrates, the resultant multiplexing-demultiplexing modules can remain stable in varying working condition.
Other objects, features, and advantages of the present invention will become apparent upon examining the following detailed description of an embodiment thereof, taken in conjunction with the attached drawings.